Conventionally, various controls of a rotary electric motor on the basis of a primary magnetic flux, i.e., a so-called primary magnetic flux controls have been proposed. Briefly speaking, the primary magnetic flux control is a technique for stably controlling the rotary electric motor by controlling the primary magnetic flux of the rotary electric motor in accordance with a command value thereof.
It is assumed, for example, that a phase of a field flux Λ0 is employed at a d axis in rotating coordinate system, a phase of a primary magnetic flux λ1 is employed at a δ axis in another rotating coordinate system, and a phase difference of the δ axis with respect to the d axis is a load angle φ. Herein, however, a γ axis is employed at a 90-degree leading phase with respect to the δ axis. Further, a δc axis and a γc axis are defined as control axes in the rotating coordinate system which is employed in the primary magnetic flux control. The δc axis and the γc axis are corresponding to the δ axis and the γ axis, respectively, and a phase difference of the δc axis with respect to the d axis is assumed as φc.
In this case, a command value of the primary magnetic flux λ1 (hereinafter, referred to as a “primary magnetic flux command value”) has a δc-axis component Λδ*, and a γc-axis component is zero. Therefore, when the primary magnetic flux λ1 is equal to the primary magnetic flux command value, the δc-axis component λ1δc of the primary magnetic flux λ1 is equal to the δc-axis component Λδ*, the phase difference φc is equal to the load angle φ, and the δc axis is coincident with the δ axis.
The δc-axis component λ1δc and the γc-axis component λ1γc of the primary magnetic flux λ1 vary with a change of the primary magnetic flux command value, a variation in a load, an influence of control disturbance, or/and the like. For example, the change of the primary magnetic flux command value and the variation in the load invites a transient change of the primary magnetic flux λ1, and the control disturbance invites a variation in the γc axis/δc axis. As states where the control disturbance occurs, for example, a state where a voltage applied to the rotary electric motor is different from a voltage command due to an influence of a time delay, an on-loss, and dead time, and a state where there is a deviation between a device constant of the rotary electric motor and that assumed by a control system. Therefore, a deviation arises between the primary magnetic flux λ1 and the primary magnetic flux command value, and accordingly a deviation also arises between the load angle φ and the phase difference φc.
In the primary magnetic flux control, when there is a deviation between the primary magnetic flux λ1 and the primary magnetic flux command value, a control, for example, of a voltage command value to be corrected is performed so that the δc-axis component λ1δc of the primary magnetic flux λ1 may be made equal to the δc-axis component Λδ* of the primary magnetic flux command value and the γc-axis component λ1γc of the primary magnetic flux λ1 may become zero. The phase difference φc is thereby coincident with the load angle φ.
In such a primary magnetic flux control, control is made with a torque of the rotary electric motor being made in direct proportion to a γc-axis component of an armature current, not depending on a rotation angular velocity thereof.
Among the following prior-art documents, in Yabe and Sakanobe, “A Sensor-less Drive of IPM Motor with Over-modulation PWM”, The papers of Joint Technical Meeting on Rotating Machinery, IEE Japan, 2001 (159), pp. 7 to 12, the γc axis and the δc axis are exchanged and employed, as compared with those in the other prior-art documents.